One-third of Americans think some UFOs that people have spotted have been alien spacecraft visiting Earth from other planets or galaxies. A 60% majority, however, believe all such sightings can be explained by human activity or natural phenomena, while an additional 7% are unsure. This is one topic on which Republicans and Democrats agree: 30% of the former and 32% of the latter describe UFOs as alien spacecraft from other planets. Belief is a bit higher among political independents, at 38%.